React Native - Device back button handling

Question

I want to check if there are more than one screens are on stack when device back button is hit. If yes, I want to show previous screen and if no, I want to exit app.

Answer 1

 import { BackHandler } from 'react-native';

 constructor() {
        super();           
        this.handleBackButtonClick = this.handleBackButtonClick.bind(this);
 }

   componentWillMount() {
       BackHandler.addEventListener('hardwareBackPress', this.handleBackButtonClick);
   }

   componentWillUnmount() {
       BackHandler.removeEventListener('hardwareBackPress', this.handleBackButtonClick);
   }

   handleBackButtonClick() {
       //this.props.navigation.goBack(null);
       BackHandler.exitApp();
       return true;
   }